This invention relates to floating equipment used in cementing operations, and to methods of drilling out float equipment to create a wellbore below a cemented casing, wherein the wellbore below the casing has a diameter larger than the inner diameter of the cemented casing.
Typically, after a well for the production of oil and/or gas has been drilled, casing will be lowered into the well and cemented in the well. Generally, casings of decreasing diameter will be used as the depth of the wellbore increases. In other words, a large diameter casing may be cemented in the uppermost portion of the wellbore, and a liner, which is simply a smaller diameter casing will extend from the lower end of the casing in the uppermost well portion. Additional liners of decreasing diameter can be cemented in the well until the desired depth is reached.
When casing is lowered into a well floating equipment, such as float shoes and float collars may be used in the casing. Typical of the float equipment that might be used is the Halliburton Super Seal II Float Collar and the Halliburton Super Seal II Float Shoe as shown in the Oct. 8, 1993, Halliburton Casing Sales Manual, pages 1-13 and 1-23, respectively. Other examples of float equipment are shown in U.S. Pat. No. 5,647,434 to Sullaway et al. and U.S. Pat. No. 5,472,035 to Sullaway et al., both of which are incorporated by reference. All of the float equipment disclosed therein has a valve affixed to an outer case, which is connected to the casing.
There are times when it is desirable to create a wellbore below the cemented casing that has a diameter greater than the inner diameter of the cemented casing. For example, there are times when it is necessary to set a liner having an outer diameter such that the wellbore in which the liner must be set is larger than the inner diameter of the casing thereabove.
When such a liner is to be placed in the well, the valve portion of the float equipment attached to the casing must be drilled out. The current practice of drilling out float equipment in the cemented casing is with a standard drill bit that has a diameter slightly less than the inner diameter of the casing string and of the outer case or outer housing of the float equipment which is attached to and forms a part of the casing. The same drill bit is sometimes used to drill ahead or past the bottom end of the float shoe to a depth that would enable another string of casing (i.e., the liner) to be run and cemented in place. If the wellbore below the casing is required to be greater than the inner diameter of the previous cemented casing, a process called underreaming is generally used. Underreaming is a process wherein the wellbore is drilled to the desired depth with the standard drill bit utilized to drill through the float equipment. That bit is removed and a special underreaming drill bit is lowered through the casing. Once the underreaming drill bit passes below the end of the casing and into the open end cased wellbore, the hole is underreamed. Thus, typically two trips are required to perform underreaming operations, one to drill through the cement plugs and float equipment and cemented casing string, as well as any open hole required to be drilled, and another special underreaming bit for underreaming operations.
Bi-center drill bits may also be used to drill the wellbore below the already cemented casing. Bi-center bits can thus be run through a specific inner diameter, for example the casing drift inner diameter, and can be rotated after passing through the casing to drill a wellbore having a diameter greater than the casing inner diameter. Bi-center drill bits have a non-working or non-rotating diameter, and have a larger working or rotating diameter. Using a bi-center bit is advantageous over underreaming since it is not required that the entire length of the wellbore be drilled with the drill bit that is utilized to drill out the float equipment. Instead, the float equipment can be drilled out to slightly below the end of the casing with a standard drill bit which can then removed from the well. The bi-center drill bit can then be utilized and can begin drilling below the bottom end of the float equipment which is part of the previously cemented casing string. While use of a bi-center bit saves some time, it still requires two trips into the well which is time consuming and costly. Thus, there is a need for a method and apparatus which will provide for one trip drilling of a wellbore below a cemented casing, wherein the wellbore below the cemented casing has a diameter larger than the inner diameter of the already cemented casing string.
The present invention solves the foregoing by providing a method and apparatus for creating a wellbore having a diameter larger than the inner diameter of a previously cemented casing in one trip.
The method comprises lowering a drill bit through cemented casing. The drill bit has a non-working or non-rotating diameter that is smaller than the inner diameter of the previously cemented casing. The casing, as is well known in the art, will typically have float equipment connected therein. The float equipment can comprise a float shoe, and/or a float collar or any other type of float equipment known in the art. The drill bit, which preferably will comprise a bi-center drill bit, will be lowered into the casing to the point at which it is desired to begin drilling of the wellbore. The drill bit is then rotated at a selected speed which will cause the drill bit to move from its non-working or non-operating position to a working or rotating position in which the drill bit will drill a hole or wellbore having a diameter greater than the inner diameter of the previously cemented casing. The drill bit is rotated in the casing at a point above the float equipment and is lowered so that it will drill out any casing therebelow along with the float equipment. The drill bit is continually lowered in its working rotating position until the desired depth of the wellbore is reached. Rotation of the drill bit may then be stopped and the drill bit withdrawn from the well through the previously cemented casing.
The floating equipment utilized with the casing comprises an outer case having a valve disposed therein. The valve is preferably connected to the outer case with a cement body portion. The outer case of the floating equipment is adapted to be connected in the casing string and preferably has threads so that it can be threaded in the casing string. The outer case is comprised of a drillable material so that the drill bit utilized to drill the wellbore below the cemented casing can drill through the float equipment including the valve, body portion and the outer case. Any tubulars or joints used between float collars and/or a float collar and the float shoe are also comprised of a drillable material.